1. Field of the Invention
The present invention relates to a vehicle-use power supply apparatus including an alternator (generator) and a battery.
2. Description of Related Art
Generally, an alternator is mounted on a vehicle for the purpose of supplying electric power to various electrical loads provided in the vehicle, and charging a vehicle battery. The alternator is driven by a vehicle engine to generate electric power. It is desirable that the increase of fuel consumption of the engine due to driving the alternator is as small as possible.
To this end, there has been proposed a technique in which a fuel consumption per unit of generated power is calculated taking account of the efficiencies of a vehicle engine and an alternator, and a generation power of the alternator and a discharge of the battery are controlled using the calculated fuel consumption as a criterion of judgment. For example, refer to Japanese Patent Applications Laid-open No. 2004-260908, and No. 2005-12971. These patent documents disclose that a power generation amount is determined on the basis of a fuel consumption per unit of generated power, and power management is performed by use of a value of electric power or power generation torque as a command value.
There is known a vehicle provided with a regenerative braking apparatus that regenerates braking energy of the vehicle to drive an alternator. However, the required electric power of the vehicle cannot be covered only by the regenerated energy. Accordingly, also in such a vehicle provided with the regenerative braking apparatus, it is desired to suppress the increase of fuel consumption of the engine due to driving the alternator.
Incidentally, it is necessary to control a voltage supplied to electrical loads provided in a vehicle within a predetermined range depending on characteristics of the electrical loads, and also to control a voltage of a vehicle battery within a predetermined range. Accordingly, to use a value of electric power or power generation torque as a command value to perform the power management as disclosed in the above patent documents, a relationship between generated electric power and an output voltage of the alternator has to be precisely known in advance. This requires preparation of a high-precision battery model, or to obtain a precise input-output characteristic of the battery.
However, actually, neither of them is not easy. Particularly, in the case of a widespread lead-acid battery, these become more difficult, because the lead-acid battery has problems of polarization and electrode degradation. Hence, although using a value of electric power or power generation torque as a command value as disclosed in the above patent documents makes it possible to improve fuel consumption, it may cause an undesirable abrupt change of the voltage supplied to electrical loads, because the voltage cannot be precisely managed.